Multiphase extrudable explosives containing cyclotrimethylenetrinitramine or cyclotetramethylenetetranitramine



United States Patent 3,480,490 MULTIPHASE EXTRUDABLE EXPLOSIVES CON-TAINING CYCLOTRIMETHYLENETRINITRA- MINE 0R CYCLOTETRAMETHYLENETETRA-NITRAMINE Milton Finger, Hayward, Edward James, Jr., Castro Valley, andPaul B. Archibald, Pleasanton, Califl, assignors to the United States ofAmerica as represented by the United States Atomic Energy Commission NoDrawing. Filed Aug. 10, 1964, Ser. No. 388,987 Int. Cl. C061) 7/00,15/00 US. Cl. 14992 14 Claims This invention was made in the course of,or under, performance of Contract No. W-7405-ENG48 with the UnitedStates Atomic Energy Commission.

The present invention relates to high explosive compositions and moreparticularly to multiphase explosive compositions especially adapted forextrusion and fabrication as by polymerization in molds.

There has long existed a need for an explosive which is sufficientlyfluid and pliable to allow transfer and shaping by extrusion methods atambient temperatures. Solid explosives are obviously not extrudable atambient temperatures. The known liquid explosives, while offering littleresistance to being transferred through conduits as in molding systems,have either a lower explosive energy density than is required for manyapplications, or are unduly sensitive and dangerous, as for instance,nitroglycerin. On the other hand, explosives which contain a solid highexplosive dispersed in an inert medium, fail to obtain the maximumenergy densities obtainable since the addition of the inertnon-explosive medium necessarily displaces some of the solid explosiveand the diminution of high explosive per unit volume goes hand in handwith a loss of explosive energy density.

If solid shapes of explosives are required, they are conventionallyformed from the more powerful explosives by machining or millingoperations which are cumbersome as well as expensive and require specialsafety precautions.

In accordance with the invention, there is now provided a high energydensity multiphase explosive composition which is especially adapted fortransfer by fluid or plastic flow into molds for forming and fabricationat low, e.g., ambient temperatures and which can be cured thereafter toproduce rigid dimensionally stable forms. More specifically, thecomposition includes selected proportions of certain solid highexplosives as a solid phase dispersed in a fluidic vehicle phase, whichitself possesses explosives characteristics as employed in the presentformulations. Certain additives may be included to control stability andthe like. Proportions are expressed in percent by weight herein unlessotherwise specified.

A primary object of the present invention is to provide an explosivecomposition which may be fabricated by processes involving fluidic orplastic flow.

Another object of the present invention is to provide a multiphaseexplosive composition having a high explosive energy content.

A further object of the present invention is to provide a multiphaseexplosive composition which is relatively insensitive to shock.

Still another object of the present invention is to provide a multiphaseexplosive composition which is extrudable and chemically stable over awide range of temperatures.

Yet another object of the present invention is to provide a multiphasehigh explosive composition which can be injected into a mold andpolymerized at low pressures.

A still further object of the present invention is to pgovide anexplosive composition which has a long shelf Other objects andadvantages will become apparent upon consideration of the followingdescription.

The solid phase of the explosive formulation of the present invention ofthe class generally characterized as a cyclicnitramine, specificallyincluding the solid explosivecyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine, hereinafterreferred to as HMX, and cyclo-l,3,5-trimethylene- 2,4,6-trinitrarnine,hereinafter referred to as RDX. The fluid in which the solid phase isdispersed is a liquid vehicle comprising one or a combination of theliquid explosives of the gem-dinitro aliphatic class, such as methyl-4,4-dinitropentanoate, ethyl 4,4-dinitropentanoate, dinitropentanonitrile, 2,2-dinitropropyl acrylate, 1,2-bis(2,2-difluoro-2-nitroacetoxyethane) and bis (2,2-dinitro-2-fluoroethyl)formal, hereinafter referred to as MDNP, EDNP, DNPN, DNPA, BEAF, andFEFO, respectively.

Compositions which are readily extrudable with low pressures include upto by weight of HMX or RDX and have a particle size of no less thanabout 2 microns with a preferred particle size of about 15-25 micronsand a maximum particle size of about 30 microns. The practical range ofHMX content lies between about 50 and 75% by weight. The composition mayalso include a stabilizer such as colloidal silica or poly-DNPA, addedto increase the stability of the composition. An explosive compositionof the above description is distinctly superior to known explosives withrespect to a combination of properties including extrudability, energydensity, and insensitivity to shock.

General preferred formulations of the multiphase explosive compositionhave an HMX content of about 65- 75 by weight, and have an HMX particlesize of about 20 microns. Variations in the HMX content and the particlesize of the HMX greatly influence three important properties of thecomposition: extrudability, energy density, and stability, orshelf-like. Regulation of the HMX content and particle size adapts thecomposition to varying requirements. The energy density of the explosiveformulation is directly proportional to the HMX content and is largelyindependent of the particle size. At HMX contents between 65 and 75 byweight, the energy density of the explosive is intermediate between thatof the high explosives trinitrotoluene (TNT), and octol (75% HMX, 25%TNT).

Concerning the relation between the HMX content, particle size, andviscosity, it has been found that the fluid or plastic flow propertiesas related to the ease of extruding of the present explosives, decreaseswith increasing HMX content and also with decreasing particle size. Withthe HMX content increased beyond 75 the HMX being present as particlesof an average diameter of about 20 microns, the viscosity rapidly risesto excessive magnitudes as represented by a flow rate of about 1 cc. persec. through a tube in. in diameter and 3 inches long at a drivingpressure of about 1000 p.s.i. Ordinarily, it is preferred that drivingpressures of up to a few hundred p.s.i. maximum are required to producetransfer of the material to fill the mold in a few seconds at the most.The stability of the solid particle phase or the tendency of the solidphase to settle out from the multiphase explosive depends on theparticle size and is inversely related to the average particle diameter.At one extreme, no phase separation or settling has been observed withHMX particles of an average diameter of about 2 microns. A dispersementof such small particles, however, severely restricts the flow rate dueto the high surface area of the solid constituent. To alleviate thisdifficulty a coarser grade HMX is used together with a stabilizer suchas colloidal silica or poly-dinitropropyl acrylate. A particle size of20 microns for the solid HMX along with 1 or 2% of colloidal silicarenders an explosive composition of satisfactory phase stability andplastic flow rate. With an intermediate particle size, correlativelylesser amounts of the stabilizer are required to provide stablemultiphase explosive formulations.

Whereas all of the fluid phase components mentioned above confer fluidicor plastic flow properties to obtaining the desired extrudability of theexplosive composition, optimum properties including the energy content,sensitivity, and the additional property of injection moldability, i.e.,introduction into a mold by a procedure involving fluid or plastic flow,depend on the particular choice of the components for the liquid phase.

Preferred major constituents of the fluid or liquid phase are EDNP,DNPN, and MDNP, used singularly or in combination with each other orwith DNPA as liquid phase vehicles for the HMX, they provide explosiveformulations which are characterized by safety from the point of view ofinsensitivity to mechanical shock and temperature variations. Forexample, drop heights for 50% explosion probability exceeded 177 cm. forsuch compositions if their HMX content is less than 75% by weight, withthe remainder being such a liquid phase and up to about 2% per weight ofa stabilizer.

The use of FEFO as the fluid for liquid phase offers a distinctadvantage in that FEFO is more energetic than the other liquidexplosives and hence provides an especially high contribution to theenergy density of the explosive. On the other hand, formulations basedon FEFO are somewhat more sensitive to shock. However, if FEFO isintermixed with one or more of the liquids, MDNP, EDNP, and DNPA, thesensitivity of the final formulation is appreciably diminished. BEAF isanother higher energy density, but also more sensitive, liquid phaseconstituent. It is to be understood that in all of the abovedescriptions, RDX can be substituted for HMX without substantialmodification.

The explosive compositions are prepared by premixing the ingredientsthoroughly. Subsequently, they are milled and deaerated by conventionaloperations as practiced in the art.

In general, the multiphase or paste explosives of the above descriptionfind use in applications where it is desired to transfer the explosiverapidly from one place of long time storage and confinement to another,e.g., immediately prior to the time of detonation to be detonated whilestill in a fluidic or paste form. In other applications, it is desirableto provide the explosive in the form of a solid body as described morefully hereinafter. An especially advantageous feature of formulationshaving a liquid vehicle phase on the energetic monomer DNPA is thatthese compositions are especially adapted for injection into a mold andsubsequent polymerization. The polymerized explosive is dense anduniform and explosive bodies made of the material are characterized byhigh mechanical strength in addition to their high explosive energydensity, stability, and safety. Moreover, the advantageous flowproperties of these explosive formulations allow their use in theformation of explosive bodies having complicated shapes of precisedimensions by a process of zone curing under pressure. To carry out thisprocess, the mixture is first deaerated and then injected from atransfer cylinder, piston or extruder into a mold under pressure. Theexplosive is cured by heating to a tempearture corresponding to theconventional curing temperatures for acrylic resins and contactlaminating resins, i.e., ambient temperatures up to about 70 C. Tocompensate for the shrinkage of the material during the solidificationproduced by curing, the mixture is cured zonewise beginning the curingprocess in those sections of the explosive body which are furtherestremoved from the injection nozzle. The mixture is kept under continuouspressure until the curing is completed. In this manner, uncured materialis continuo y ntro c d into the volume vacated by the receding body ofthe curing or setting material and hence offsets the shrinkage effects,since no voids are allowed to develop.

Specifically, multiphase explosive compositions which are injectionmoldable and polymerizable under low pressure comprise the solidexplosive HMX in proportions of about by weight to by weight and aliquid phase vehicle comprising one or more of the liquid explosivesMDNP, EDNP, DNPN, BEAF and FE'FO, and/ or at least about 15% of DNPA.They may also include a dispersion agent, such as colloidal silica up toabout 2% by weight and small amounts of cross linking agents, typicallyfractions of a percent, such as diand triacrylates, i.e., acrylateesters containing two, three, or more unsaturated double bond linkages.Inasmuch as the cross linking agents are present in small quantitiesonly, any equivalent nonenergetic or reagent producing this result maybe substituted without impairing the energy density of the formulationappreciably. Finally, the composition may include small amounts ofcatalysts, generally of the free radical initiator type, e.g., organicperoxides such as benzoyl peroxide, methyl ethyl ketone peroxide, etc.

While such injection moldable, low pressure polymerizable formulationsare generally subject to the same principles elaborated above withrespect to extrudability, sensitivity and explosive energy density,phase stability demands are much less stringent. The settling rate ofthe solid explosive particles has to be only sufiiciently slow toprevent separation during the comparatively short time between themixing of the explosive and completion of the molding and polymerizationprocess. Consequently, it is possible to increase the particle size ofthe HMX and hence also the HMX content to yield a maximum viscositylimit imposed by retention of adequate extrudability for carrying outthe injection process.

If some of the DNPA is added in prepolymerized form rather than as themonomer, the shrinkage of the explosive body during the curing can bereduced. In this manner, it is possible to control the overalltolerances attainable and the ease with which the process can be carriedout.

EXAMPLES The procedure for mixing the ingredients of the followingexamples was in each case a preliminary mixing of the ingredients in avertical planetary motion propeller type mixer. The premixed dispersionwas then passed three times through a 3 roll paint mill. In each casethe air was removed from the mixture by passing it through a ram-orificedeaerator after which the explosive was ready for use.

- EXAMPLE I Composition:

HMX, average particle size about 20 microns percent 73 EDNP do 22.1 MDNPdo 3.9 Colloidal SiO do 1 1 Ethyl4,4-dinitropentanoate-2-methyl-4,4-dinit1'0penton0ate. Properties:

Density g./cc 1.673 Detonation velocity mm./m. sec 7.84

EXAMPLE II Composition:

HMX percent 71.45 DNPN 1 do 27.06 Colloidal SiO do 1.49

1 Dinitropeutano nitrile.

Properties:

Density g./cc 1.70 Detonation velocity ,mm./rn, sec 7.98

EXAMPLE III Composition:

HMX percent 67.67 BEAF 1 do 30.92 Colloidal Si0 do 1.41

1 1,2-bis (2,2 diflu0ro-2-nitroacetoxyethane) Properties:

Density ...g./cc 1.79 Detonation velocity mm./m. sec 8.15

EXAMPLE IV Composition:

HMX percent 67.54 FEFO 1 do 31.05 Colloidal SiQ do 1.41 1 Bis(2,2-dinitr02-flu0ro ethyl) formal. Properties:

Density g./cc 1.79 Detonation velocity mm./m. sec 8.44

EXAMPLE V Composition:

HMX percent 70 DNPA 1 do EDNP 2 do 7 Dimethacrylate do 1 Benzoylperoxide do 1/10 1 2,2-dinitr0pr0pyl acrylate.

9 Ethyl 4,4-dinitropentanoate.

After mixing, milling, and deaerating this composition as elaborated inthe preamble of the examples, the mixture is injected under a pressureof 50-200 p.s.i. through an inch orifice into the mold of the desiredshape of the final explosive body, e.g., a 1 m. long rod of diameter.While under continuous pressure, the mold is heated to 4060 C. for about40 minutes per zone, of a ZOne several cm. in length moved progressivelyalong the mold beginning at the zone furthest removed from the injectionnozzle. The entire process is completed in about 2 hours.

We claim:

1. A multiphase explosive composition of matter comprising a solid phaseof powdered explosive material selected from the group consisting ofcyclo-1,3,5,7-tetramethylene-2,4,6,8 tetranitramine andcyclo-1,3,5-trimethylene-2,4,6-trinitramine and a liquid phasecomprising at least one material selected from the group consisting ofmethyl-4,4-dinitropentanoate, 2,2-dinitropropyl acrylate, dinitropentanonitrile, ethyl-4,4-dinitropentanoate, and his(2,2-dinitro-2-fluoroethyl) formal; said cyclo-1,3,5,7-tetramethylene2,4,6,8 tetranitramine being dispersed throughout said liquid.

2. The composition of claim 1 wherein said powdered explosive has anaverage particle diameter of at least 2 microns.

3. The composition of claim 1 wherein said powdered explosive has anaverage particle diameter of about 20 microns.

4. The composition of claim 1 wherein there is included a stabilizingagent.

5 The composition of claim 4 wherein said stabilizing agent is selectedfrom the group consisting of colloidal silica and poly-dinitropropylacrylate.

6. A multiphase explosive composition comprising a solid phase selectedfrom the group consisting of cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine and cyclo-1,3,5-trimethylene-2,4,6-trinitramine and a liquid phase comprising atleast about 40% by weight bis(2,2-dinitro-2- fluoroethyl)formal and atleast one liquid selected from the group consisting ofmethyl-4,4-dinitropentanoate, dinitropentanonitrile, andethyl-4,4-dinitropentanoate.

7. A polymerizable multiphase explosive composition comprising a solidphase selected from the group consisting ofcyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine and cyclo 1,3,5trimethylene 2,4,6 trinitramine and a liquid phase comprising2,2-dinitropropyl acrylate.

8. The explosive composition of claim 7 further defined by including atleast one explosive selected from the group comprisingmethyl-4,4-dinitropentanoate; dinitro pentanonitrile;ethyl-4,4-dinitropentanoate; bis(2,2-dinitro-2-fluoroethyl) formal, and1,2-bis(2,2-difluoro-2-nitroacetoxy) ethane.

9. The composition according to claim 7 wherein the composition includesa dispersing agent.

10. The composition according to claim 7 wherein the compositionincludes prepolymerized 2,2-dinitropropyl acrylate.

11. The composition of claim 7 wherein the composition includes acrosslinking agent.

12. The composition of claim 10 wherein the crosslinking agents areselected from the group consisting of diand tri-acrylates.

13. The composition of claim 7 wherein said solid phase is between 50and by weight. I

14. The composition of claim 7 wherein said 2,2-dinitropropyl acrylateis at least 15% by weight.

No references cited BENJAMIN R. PADGETT, Primary Examiner S. J. LECHERT,JR., Assistant Examiner US. Cl. X.R.

1. A MULTIPHASE EXPLOSIVE COMPOSITION OF MATTER COMPRISING A SOLID PHASEOF POWDERED EXPLOSIVE MATERIAL SELECTED FROM THE GROUP CONSISTING OFCYCLO-1,3,5,7-TETRAMETHYLENE-2,4,6,8-TETRANITRAMINE ANDCYCLO-1,3,5-TRIMETHYLENE-2,4,6-TRINITRAMINE AND A LIQUID PHASECOMPRISING AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OFMETHYL-4,4-DINITROPENTANOATE, 2,2-DINITROPROPYHL ACRYLATE,DINITROPENTANO NITRILE, ETHYL-4,4-DINITROPENTANOATE, AND BIS(2,2-DINITRO-2-FLUOROETHYL) FORMAL; SAID CYCLO-1,3,5,7-TETRAMETHYLENE -2,4,6,8 - TETRANITRAMINE BEING DISPERSED THROUGHOUT SAID LIQUID.